Asked by: Duncan Simmons, Plymouth
Astronomers recently found that the atmosphere of Uranus has high levels of hydrogen sulphide, a compound that smells like rotten eggs. The only first-hand account of the smell of another celestial body came from the Apollo astronauts, who claimed that Moon dust smelt like spent gunpowder. Mercury has a very sparse atmosphere and so would not have much of a smell at all. Venus and Mars, much like Uranus, have substantial quantities of eggy hydrogen sulphide.
For Jupiter, the smell would depend on where you were in the atmosphere. Some regions have high concentrations of ammonia (which smells like cleaning fluid), others hydrogen sulphide (eggs) and others hydrogen cyanide (bitter almonds). Saturn and Neptune probably don’t have much of a smell because they’re composed chiefly of the odourless gases hydrogen and helium.